All CSS Instead?

Some Web standards professionals recommend using CSS formatting instead the <sup> and <sub> tags on the theory that these tags are "presentational." The disadvantage to this approach is that if a user disables your stylesheet, the superscripts and subscripts will disappear.

However, if you are more comfortable with using the CSS attributes, you can refer to these pages.

Using Unicode Values

Many common superscript and subscript characters have their own Unicode entries and entity codes. If your Web page is generated from a database or meant to be a searchable archive, the use of Unicode values may be preferable.